1. Field of the Invention
The present invention relates to a method for regenerating supported iridium-containing hydrocarbon conversion catalysts. More particularly, the present invention relates to a multi-step process sequence for regenerating a supported iriduim-containing hydrocarbon conversion catalyst that has been at least partially deactivated because of the presence of the iridium in the catalyst in a large crystallite, low surface area form.
2. Description of the Prior Art
The deactivation of noble metal-containing hydrocarbon conversion catalyst due to the deposition on the catalyst of carbonaceous residues is a common refinery problem. Catalyst deactivation is particularly acute with respect to supported noble metal-containing catalysts, such as platinum on alumina, employed in the hydroforming of naphtha feed stocks. Platinum-containing reforming catalysts are reactivated or regenerated by burning the coke or carbonaceous residues from the catalyst followed by a redispersion operation whereby the platinum contained on the catalyst, which is agglomerated with loss of surface area during the burning operation, is redispersed by treatment with chloride or other halogen-providing reagents, along or in combination with oxygen at elevated temperatures. The techniques useful for the reactivation of platinum-containing catalysts, such as those disclosed in U.S. Pat. Nos. 3,134,732 and 3,625,860, are not directly applicable for the redispersion of iridium. Unlike platinum, iridium tends to agglomerate to crystallites of low surface area when exposed to oxygen at temperatures in excess of about 700.degree. F. Further, unlike platinum, large iridium and iridium oxide crystallites are not readily redispersed to their high surface area state by a simple chloride treatment immediately following the burning operation used to remove carbonaceous residues.
It has been discovered that iridium present on a supported catalyst can be redispersed to a high surface area state by contacting the catalyst, after the removal of carbonaceous residues, by subjecting the catalyst to one or more sequential reduction/halogenation cycles. Ordinarily a plurality of such reduction/halogenation cycles are needed to completely redisperse the iridium. Because of the time involved in subjecting the catalyst to a plurality of such reduction/halogenation cycles and the corrosive nature of such treatment operations, it is desirable that a number of such reduction/halogenation cycles to which the catalyst is subjected be held to a minimum.